Method of opening a packing box

ABSTRACT

A packing box enables easy release a slit lock in which slits in an insertion piece of an openable lid engage side flaps connected to openable lid side edge portions of lid side members, even if the interior of a box body of the packing box is tightly filled with a product. The top face lid of the packing box includes a part that can be torn along a tear inducing line extending from the flap opposing edge of the top face lid to the front end edge of the top face lid. This part is held and torn along the tear inducing line by a human hand, and is raised up with respect to the top face lid to form the slit lock release gripping piece that can be used for releasing engagement created by the slit lock engaging structure, so that the engagement by the slit lock engaging structure, which is the engagement between the insertion piece and the side flap in the slit on the side in the lateral direction of the insertion piece where the slit lock release gripping piece is formed, can be easily released even if the interior of the box body of the packing box is tightly filled.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. patent application Ser. No. 15/307,387, filedon Oct. 28, 2016, the disclosure of which is here incorporated byreference. This application claims domestic priority on the basis ofapplication Ser. No. 15/307,387, filed on Oct. 28, 2016, andInternational Patent Application PCT/JP2015/062885, filed on Apr. 28,2015, and foreign priority on the basis of Japanese patent application2014-093636, filed on Apr. 30, 2014 and Japanese patent application2014-129844, filed on Jun. 25, 2014.

FIELD OF THE INVENTION

The invention relates to a packing box forming a slit lock engagingstructure for retaining a state in which an openable lid is closed byengaging a portion of a side flap into a slit created by partiallycutting a connection base end of an insertion piece along a foldingline. Particularly, the invention relates to a packing box that packs aproduct such as a cosmetic, drug, food, or toy, or a fancy box thathouses the product and is displayed on a sales floor, such as a storefront, for protecting the product or the fancy box from being damaged orimpacted during delivery of the product or the fancy box to the salesfloor.

BACKGROUND OF THE INVENTION

As one example of the packing box, a packing case is conventionallyknown that includes an arc-like cutout portion formed at an upper end ofa front face of box body overlapping an insertion piece and a push-inpiece formed at a portion of the box body facing the cutout portion andsurrounded with an arc-like cut so that a finger hook hole can becreated, wherein the packing case is opened by hooking a finger into thefinger hooking hole and pulling up a lid portion. See, for example,Japanese Laid-Open Patent Application No. 2007-253966, particularlyFIGS. 1 to 3.

As another example of the packing box, an article storage box is knownthat includes cut lines (slits) provided at both ends of a borderbetween a lid plate and an insertion piece and side flaps, wherein thearticle storage has a so-called slit lock structure in which the sideflaps are hooked into the cut lines (slits). See, for example, JapaneseLaid-Open Patent Application No. 2001-301741, particularly FIG. 1, andJapanese Laid-Open Patent Application No. 2007-209598, particularlyFIGS. 1 and 2.

As another example of the packing box, a sealed box is known thatincludes locking cuts formed at both end portions of a lateral foldingline between a top face flap piece and a top face insertion flap pieceand constituting a lock mechanism, locking projection pieces formed atbase ends of inner top face flap pieces and constituting the lockmechanism, and a flange formed at a center portion of the top face flappiece and used as a start portion of tearing along tear inducing lines.See, for example, Japanese Laid-Open Patent Application No. 2013-1424,particularly FIGS. 1 to 3.

In a state in which the top face flap piece closes an opening of atubular body, the top face insertion flap piece is anchored by insertinglocking projection pieces into the locking cuts so that the state inwhich the top face flap piece closes the opening is maintained. Anarticle stored in the sealed box can be taken out by tearing along thetear inducing lines.

As another example of the packing box, a paper box is known that locks alid plate in a closed state by engaging base portions at both ends of aninsertion piece to front edge portions of lid pieces (side flaps). See,for example, Japanese Laid-Open Patent Application No. 2002-19766,particularly, FIGS. 1 to 10. The paper box is opened by pushing apush-in portion, which is formed at a front portion of the lid platewith a folding line or a cut line, by a finger to create a depressedarea and then inserting the finger into the depressed area to lift upthe lid plate by the finger to unlock the lid plate.

However, because the conventional packing case of Japanese Laid-OpenPatent Application No. 2007-253966 has a structure in which the fingerhook hole is created by pushing the push-in piece into the interior ofthe box body, the finger hook hole cannot be created for opening the lidportion when the interior of the box body is tightly filled with a fancybox or the like.

Also, because the conventional article storage box described in JapaneseLaid-Open Patent Applications Nos. 2001-301741 and 2007-209598, has thestructure in which the lid plate is opened by inserting a finger betweenthe front plate and the insertion piece for deflecting the insertionpiece to unhook the side flaps from the cut lines (slits), it isdifficult to open the lid plate to take a fancy box or the like out ofthe article storage box when the interior of the box body is tightlyfilled with the fancy box or the like so that a finger cannot beinserted between the front plate and the insertion piece for deflectingthe insertion piece.

Also, because the sealed box described in Japanese Laid-Open PatentApplication No. 2013-1424 has the structure in which a part of the topface flap piece is opened by tearing from the flange without unlockingthe lock mechanism, it is difficult to take a fancy box or the like outof the sealed box when the interior of box body is tightly filled withthe fancy box or the like, since the fancy box or the like gets caughton the rest of the top face flap piece.

Also, because the paper box described in Japanese Laid-Open PatentApplication No. 2002-19766 has the structure in which the push-inportion is pushed by a finger for opening the lid plate, it is difficultto take a fancy box or the like out of the paper box when the interiorof box body is tightly filled with the fancy box or the like, since thepush-in portion cannot be pushed by a finger in the first place.

Meanwhile, a suspended packing box is known that includes a suspensionpiece having a suspension hole formed with a separation line, such as aperforation line or a tear line, which extends from one side edge of anupper lid to a back face side of the upper lid. See for example JapaneseLaid-Open Patent Application No. H10-77029, particularly, FIGS. 2 to 4.However, the separation line is provided for simply forming a part ofthe upper lid as the suspension piece and has nothing to do with openingthe upper lid.

SUMMARY OF THE INVENTION

Thus, the object of this invention is to address the above describedproblems, and to provide a packing box that can easily release a slitlock in which slits of an insertion piece of an openable lid engage withside flaps connected to openable lid side edge portions of lid sidemembers, even if the interior of a box body of the packing box istightly filled with a product.

According to a first aspect of the invention, the above-describesproblems are addressed by providing a packing box including an openablelid that constitutes at least one face of a box body, which is apolyhedron to house a product, and openably and closably swings around abase end to seal a product taking-in/out opening formed at a position ofthe one face, a side flap that is laterally located with respect to theopenable lid and is connected via a folding line to an openable lid sideedge portion of a lid side member constituting a part of the polyhedronfor preventing protrusion of the product, and an insertion piece that isconnected to a front end edge of the openable lid via a folding line andis inserted into the box body for holding the openable lid, the packingbox constituting a slit lock engaging structure that maintains a statein which the openable lid is closed by engaging a part of the side flapinto a slit created by cutting a part of a connection base end of theinsertion piece along the folding line, wherein the openable lidincludes a part that can be torn along a tear inducing line extendingfrom a flap opposing edge of the openable lid opposing the side flap toa front end edge of the openable lid, and the part is held and tornalong the tear inducing line by a human hand and is raised up withrespect to the openable lid to form a slit lock release gripping piecethat can be used for releasing engagement created by the slit lockengaging structure.

According to a second aspect of the invention, the above-describesproblems are further addressed by providing the packing box according tothe first aspect, wherein the slit includes a L-shaped cut formed bycutting from a start point on a folding line, which is a border betweenthe insertion piece and the openable lid, toward a side of the insertionpiece for a length that is at least equal to a thickness of the sideflap and then cutting toward a side end of the insertion piece, and theinsertion piece is folded with respect to the openable lid for formingthe slit, and a part of the openable lid projecting forward from thefolding line when the insertion piece is folded with respect to theopenable lid forms an unlock projection piece that is able to abutagainst the side flap in the slit when the slit lock release grippingpiece is raised up to release the engagement created by the slit lockengaging structure.

According to a third aspect of the invention, the above-describesproblems are further addressed by providing the packing box according tothe first or second aspect, wherein the tear inducing line is formed inan arc-like shape that is orthogonal to the flap opposing edge and thefront end edge of the openable lid.

According to a fourth aspect of the invention, the above-describesproblems are further addressed by providing the packing box according tothe third aspect, wherein the arc-like shape of the tear inducing lineis an arc of a precise circle whose center is located at a cross-pointof the front end edge and the flap opposing edge of the openable lid.

According to a fifth aspect of the invention, the above-describesproblems are further addressed by providing the packing box according tothe third aspect, wherein an open window is formed on any one face ofthe polyhedron.

According to a sixth aspect of the invention, the above-describesproblems are further addressed by providing the packing box according tothe third aspect, wherein at least one of the slit lock release grippingpiece and the side flap has a temporary gluing portion on a face thereofopposing the other of the slit lock release gripping piece and the sideflap, the temporary gluing portion including a glue applied thereto forgluing to, removing from, and regluing to the other of the slit lockrelease gripping piece and the side flap.

According to a seventh aspect of the invention, the above-describesproblems are further addressed by providing the packing box according tothe third aspect, wherein a cutout portion is provided in an upper endportion of a front wall plate member constituting at least one face ofthe box body so as to oppose the tear inducing line at the front endedge of the openable lid.

Because the packing box of the invention includes an openable lid thatconstitutes at least one face of a box body, which is a polyhedron tohouse a product, and openably and closably swings around a base end toseal a product taking-in/out opening formed at a position of the oneface, a side flap that is laterally located with respect to the openablelid and is connected via a folding line to an openable lid side edgeportion of a lid side member constituting apart of the polyhedron forpreventing protrusion of the product, and an insertion piece that isconnected to a front end edge of the openable lid via a folding line andis inserted into the box body for holding the openable lid, the packingbox constituting a slit lock engaging structure that maintains a statein which the openable lid is closed by engaging a part of the side flapinto a slit created by cutting a part of a connection base end of theinsertion piece along the folding line, the packing box not onlyprevents the openable lid from being opened accidentally but also hasthe following unique effects.

According to the packing box of the first aspect of the invention,because the openable lid includes apart that can be torn along a tearinducing line extending from a flap opposing edge of the openable lidopposing the side flap to a front end edge of the openable lid, and thepart is held and torn along the tear inducing line by a human hand andis raised up with respect to the openable lid to form a slit lockrelease gripping piece that can be used for releasing engagement createdby the slit lock engaging structure, the slit lock release grippingpiece is torn from the flap opposing edge of the openable lid along thetear inducing line and is raised up due to a pulling force in upward andforward directions created by a human hand when the openable lid isopened, the upward direction being the direction in which the openablelid opens, and the insertion piece is also pulled upward and forward asthe slit lock release gripping piece is pulled upward and forward by ahuman hand so that the slit at a side of the insertion piece in alateral direction of the insertion piece where the slit lock releasegripping piece is formed moves forward with respect to the side flap,allowing the side flap to be taken out of the slit and the slit to movein the upward direction. Thus, the engagement by the slit lock engagingstructure, which is the engagement between the insertion piece and theside flap in the slit on the side in the lateral direction of theinsertion piece where the slit lock release gripping piece is formed,can be easily released even if the interior of the box body of thepacking box is tightly filled.

According to the packing box of the second aspect of the invention,because the slit includes a L-shaped cut formed by cutting from a startpoint on a folding line, which is a border between the insertion pieceand the openable lid, toward a side of the insertion piece for a lengththat is at least equal to a thickness of the side flap and then cuttingtoward a side end of the insertion piece, and the insertion piece isfolded with respect to the openable lid for forming the slit, and a partof the openable lid projecting forward from the folding line when theinsertion piece is folded with respect to the openable lid forms anunlock projection piece that is able to abut against the side flap inthe slit when the slit lock release gripping piece 111 e is raised up torelease the engagement created by the slit lock engaging structure, theunlock projection piece swings around the folding line to push the sideflap out of the slit when the slit lock release gripping piece is raisedup. Thus, the engagement by the slit lock engaging structure, which isthe engagement between the insertion piece and the side flap in the sliton the side in the lateral direction of the insertion piece where theslit lock release gripping piece is formed, can be reliably released.

According to the packing box of the third aspect of the invention,because the tear inducing line is formed in an arc-like shape that isorthogonal to the flap opposing edge and the front end edge of theopenable lid, the direction of a stress acting on the tear inducing linegradually changes from the direction orthogonal to the flap opposingedge of the openable lid to the direction orthogonal to the front endedge of the openable lid when a part of the openable lid is raised upfrom the flap opposing edge by a human hand, and the point on which thestress acts does not stay on a single location on the tear inducing linebut moves gradually from the flap opposing edge to the front end edge ofthe openable lid in an arc-like manner. Thus, the slit lock releasegripping piece can be formed by tearing along the tear inducing linesmoothly.

According to the packing box of the fourth aspect of the invention,because the arc-like shape of the tear inducing line is an arc of aprecise circle whose center is located at a cross-point of the front endedge and the flap opposing edge of the openable lid, the amount of thestress acting along the tear inducing line is substantially equalized inaccordance with the radius of the precise circle and a load acting froma human hand is also substantially equalized when a part of the openablelid is raised up from the flap opposing edge of the openable lid by ahuman hand. Thus, the slit lock release gripping piece can be formed bytearing along the tear inducing line more smoothly.

According to the packing box of the fifth aspect of the invention,because an open window is formed on any one face of the polyhedron, aproduct housed in the packing box can be seen from outside through theopen window. Thus, a user can check the product. Also, the bar code ofproduct information written on the product housed in the packing box canbe seen from outside through the open window. Thus, a person in chargeof product inspection, for example, can inspect the product.

According to the packing box of the sixth aspect of the invention,because at least one of the slit lock release gripping piece and theside flap has a temporary gluing portion on a face thereof opposing theother of the slit lock release gripping piece and the side flap, thetemporary gluing portion including a glue applied thereto for gluing to,removing from, and regluing to the other of the slit lock releasegripping piece and the side flap, the slit lock release gripping pieceis temporarily glued in a position that is in the same plane as theopenable lid. Thus, the slit lock release gripping piece can be returnedto the position that is in the same plane as the openable lid even afterthe packing box is opened for continuously using the packing box, andthe slit lock can be re-released as need arises.

According to the packing box of the seventh aspect of the invention,because a cutout portion is provided in an upper end portion of a frontwall plate member constituting at least one face of the box body so asto oppose the tear inducing line at the front end edge of the openablelid, a portion of the front wall plate member near the slit lock releasegripping piece can easily deflect forward and the insertion piece can beeasily displaced forward when the slit lock release gripping piece ispulled upward and forward by the pulling force. Thus, the engagement bythe slit lock engaging structure on the side in the lateral direction ofthe insertion piece where the slit lock release gripping piece is formedcan be released more easily.

Also, because the cutout portion is provided in the upper end portion ofthe front wall plate member constituting at least one face of the boxbody so as to oppose the tear inducing line at the front end edge of theopenable lid, stress acting on an end point of the tear inducing line,which is a joint portion between the slit lock release gripping pieceand the insertion piece, is dispersed when the slit lock releasegripping piece is pulled upward and forward by the pulling force. Thus,a break that tends to occur at this point can be suppressed to morereliably release the engagement between the insertion piece and the sideflap in the slit created by the slit lock engaging structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view schematically illustrating thepacking box of a first embodiment of the invention.

FIG. 2 is a development view of the packing box of the first embodimentof the invention.

FIG. 3A is a front perspective view illustrating the behavior of theslit lock release gripping piece of the invention.

FIG. 3A is a rear perspective view illustrating the behavior of the slitlock release gripping piece of the invention.

FIG. 4A is a front perspective view illustrating the behavior of theslit lock release gripping piece of the invention.

FIG. 4B is a rear perspective view illustrating the behavior of the slitlock release gripping piece of the invention.

FIG. 5A is a front perspective view illustrating the behavior of theslit lock release gripping piece of the invention.

FIG. 5B is a rear perspective view illustrating the behavior of the slitlock release gripping piece of the invention.

FIG. 6A is a front perspective view illustrating the behavior of theslit lock release gripping piece of the invention.

FIG. 6B is a rear perspective view illustrating the behavior of the slitlock release gripping piece of the invention.

FIG. 7A is a front perspective view illustrating the behavior of theslit lock release gripping piece of the invention.

FIG. 7B is a rear perspective view illustrating the behavior of the slitlock release gripping piece of the invention.

FIG. 8 is a front perspective view illustrating the state in which theopenable lid of the packing box of the invention is open.

FIG. 9A is a sectional side view as seen in the direction indicated withreference numerals 9A-9A in FIG. 1.

FIG. 9B is a sectional side view as seen in the direction indicated withreference numerals 9B-9B in FIG. 3A.

FIG. 9C is a sectional side view as seen in the direction indicated withreference numerals 9C-9C in FIG. 5A.

FIG. 10 is a perspective view schematically illustrating the packing boxof a second embodiment of the invention.

FIG. 11 is a development view of the packing box of the secondembodiment of the invention.

FIG. 12 is a perspective view schematically illustrating the packing boxof a third embodiment of the invention.

FIG. 13 is a development view of the packing box of the third embodimentof the invention.

FIG. 14 is a perspective view schematically illustrating the packing boxof a fourth embodiment of the invention.

FIG. 15 is a development view of the packing box of the fourthembodiment of the invention.

FIG. 16 is a front perspective view schematically illustrating thepacking box of a fifth embodiment of the invention.

FIG. 17 is a development view of the packing box of the fifth embodimentof the invention.

FIG. 18A is a front perspective view illustrating the behavior of theslit lock release gripping piece of the fifth embodiment.

FIG. 18B is a rear perspective view illustrating the behavior of theslit lock release gripping piece of the fifth embodiment.

FIG. 19A is a front perspective view illustrating the behavior of theslit lock release gripping piece of the fifth embodiment.

FIG. 19B is a rear perspective view illustrating the behavior of theslit lock release gripping piece of the fifth embodiment.

FIG. 20A is a front perspective view illustrating the behavior of theslit lock release gripping piece of the fifth embodiment.

FIG. 20B is a rear perspective view illustrating the behavior of theslit lock release gripping piece of the fifth embodiment.

FIG. 21A is a front perspective view illustrating the behavior of theslit lock release gripping piece of the fifth embodiment.

FIG. 21B is a rear perspective view illustrating the behavior of theslit lock release gripping piece of the fifth embodiment.

FIG. 22A is a front perspective view illustrating the behavior of theslit lock release gripping piece of the fifth embodiment.

FIG. 22B is a rear perspective view illustrating the behavior of theslit lock release gripping piece of the fifth embodiment.

FIG. 23 is a front perspective view illustrating the state in which thetop face lid, which is the openable lid of the packing box of the fifthembodiment, is open.

FIG. 24A is a sectional side view as seen in the direction indicatedwith reference numerals 24A-24A in FIG. 16.

FIG. 24B is a sectional side view as seen in the direction indicatedwith reference numerals 24B-24B in FIG. 18A.

FIG. 24C is a sectional side view as seen in the direction indicatedwith reference numerals 24C-24C in FIG. 19A.

FIG. 25A is a front perspective view illustrating the packing box of asixth embodiment.

FIG. 25B is a front perspective view illustrating the packing box of aseventh embodiment.

FIG. 26 is a development view of the upper portion of the packing box ofan eighth embodiment of the invention.

DETAILED DESCRIPTION

Details of embodiments of the invention do not matter as long as thepacking box provided by the invention includes an openable lid thatconstitutes at least one face of a box body, which is a polyhedron tohouse a product, and openably and closably swings around a base end toseal a product taking-in/out opening formed at a position of the oneface, a side flap that is laterally located with respect to the openablelid and is connected via a folding line to an openable lid side edgeportion of a lid side member constituting a part of the polyhedron forpreventing protrusion of the product, and an insertion piece that isconnected to a front end edge of the openable lid via a folding line andis inserted into the box body for holding the openable lid, the packingbox constituting a slit lock engaging structure that maintains a statein which the openable lid is closed by engaging a part of the side flapinto a slit created by cutting a part of a connection base end of theinsertion piece along the folding line, wherein the openable lidincludes a part that can be torn along a tear inducing line extendingfrom a flap opposing edge of the openable lid opposing the side flap toa front end edge of the openable lid, and the part is held and tornalong the tear inducing line by a human hand and is raised up withrespect to the openable lid to form a slit lock release gripping piecethat can be used for releasing engagement created by the slit lockengaging structure, so that the engagement by the slit lock engagingstructure, which is the engagement between the insertion piece and theside flap in the slit on the side in the lateral direction of theinsertion piece where the slit lock release gripping piece is formed,can be easily released even if the interior of the box body of thepacking box is tightly filled.

For example, the packing box may have a shape of a polyhedron such ascube, cuboid, polygonal prism such as hexagonal prism, deltahedron,Platonic solid, or Archimedean solid, and faces of the polyhedron mayinclude one or more types of shapes or sizes, as long as the packing boxhas the slit lock engaging structure in which a part of a side flapengages into a slit of an insertion piece connected to a front end sideof an openable lid, and at least one face of the polyhedron constitutesthe openable lid.

The openable lid may be plural. Also, the openable lid may be consist ofa single face of the polyhedron, or may be consist of adjacent multiplefaces of the polyhedron.

The slit may be a slit that is created with a simple partial cut line,and a slit that is created so as to have a certain amount of width, aswith a cutout.

Also, the material of the packing box may be a paper, such as a coatedpaper, a cardboard, or a coated cardboard, or a resin such as a plastic,as long as the material has enough flexibility for forming a polyhedron.

Also, the tear inducing line may be straight or arc-like, as long as thetear inducing line extends from the flap opposing edge of the openablelid to the front end edge of the openable lid.

Also, the tear inducing line may be a perforated line or a cut line,which is created by making small cuts along a desired line inpredetermined intervals for easy tearing, or may be created by makingthe portion of the desired line thinner than the other portions so thattearing along the desired line can be easily executed.

A packing box 100 of a first embodiment of the invention will now bedescribed with reference to FIGS. 1 to 9.

FIG. 1 is a front perspective view schematically illustrating thepacking box 100 of first embodiment of the invention. FIG. 2 is adevelopment view of the packing box 100 of the first embodiment of theinvention. FIGS. 3A, 4A, 5A, 6A, and 7A are front perspective viewsillustrating the behavior of a slit lock release gripping piece 111 e ofthe invention. FIGS. 3B, 4B, 5B, 6B, and 7B are rear perspective viewrespectively corresponding to FIGS. 3A, 4A, 5A, 6A, and 7A. FIG. 8 is afront perspective view illustrating a state in which an openable lid 111of the packing box 100 of the invention is open. FIG. 9A is a sectionalside view as seen in the direction represented with reference numerals9A-9A in FIG. 1. FIG. 9B is a sectional side view as seen in thedirection represented with reference numerals 9B-9B in FIG. 3A. FIG. 9Cis a sectional side view as seen in the direction represented withreference numerals 9C-9C in FIG. 5A.

As illustrated in FIGS. 1 and 2, the packing box 100 of the firstembodiment of the invention is made of a thick coated cardboard, andincludes a box body 110 that is an inverted quadrangular pyramid(pentahedron) as one example of a polyhedron having the openable lid 111and being capable of housing a fancy box (not shown) as one example of aproduct, an insertion piece 120 that holds the openable lid 111, andleft and right side flaps 130 and 140 as side flaps.

The openable lid 111 constitutes one face of the box body 110 that is aninverted quadrangular pyramid, and is provided so as to openably andclosably swing around an openable base end folding ruled line BL1, whichis a folding line, at a base end 111 a to seal a product taking-in/outopening EE (see FIG. 8) formed at a position of the one face. Theinsertion piece 120 is mutually connected to a front end edge 111 c ofthe openable lid 111 via an openable front end edge folding ruled lineBL2, which is a folding line, and is provided so as to be inserted intothe box body 110 to hold the openable lid 111.

The left side flap 130 is configured so as to mutually connect to a leftside wall plate member 113, which is a lid side member located at a sidewith respect to the openable lid 111 and constitutes a part of theinverted quadrangular pyramid, via a left side wall upper end foldingruled line BL3, which is a folding line, at an openable lid side edgeportion of the left side wall plate member 113 to prevent protrusion ofthe product. Similar to the left side flap 130, the right side flap 140is configured so as to mutually connect to a right side wall platemember 115, which is a lid side member located at a side with respect tothe openable lid 111 and constitutes a part of the inverted quadrangularpyramid, via a right side wall upper end folding ruled line BL4, whichis a folding line, at an openable lid side edge portion of the rightside wall plate member 115 to prevent protrusion of the product.

In the description of the present embodiment, for the purpose ofillustration, the upside of the packing box 100 is where the openablelid 111 is located, the front side of the packing box 100 is where afront end edge 111 c, which is a free end of the openable lid 111, islocated, and the rear side of the packing box 100 is where the base end111 a is located. Also, “left” and “right” are defined with respect tothe packing box 100 that has been constructed. In other words, “left”and “right” are left and right of the packing box 100 as seen from arear wall plate member 112 toward a front wall plate member 114 of thepacking box 100.

As illustrated in FIG. 2, the box body 110 having a shape of an invertedquadrangular pyramid includes the openable lid 111, the rear wall platemember 112, the left side wall plate member 113 as a lid side member,the front wall plate member 114, the right side wall plate member 115 asa lid side member, and a right side rear margin 116. The rear wall platemember 112 is connected to the base end 111 a of the openable lid 111via the openable base end folding ruled line BL1, which is a foldingline. The left side wall plate member 113 is connected to a left endportion of the rear wall plate member 112 via a rear wall left endfolding ruled line BL5, which is a folding line.

The front wall plate member 114 is connected to a front end of the leftside wall plate member 113 via a left side wall front end folding ruledline BL6, which is a folding line. The right side wall plate member 115is connected to a right end portion of the front wall plate member 114via a front wall right end folding ruled line BL7, which is a foldingline. The right side rear margin 116 is connected to a rear end portionof the right side wall plate member 115 via a right side wall rear endfolding ruled line BL8, which is a folding line.

When the packing box 100 is constructed, the rear wall plate member 112or the left side wall plate member 113 is folded along the rear wallleft end folding ruled line BL5 so that an angle therebetween becomes 90degrees, and the left side wall plate member 113 or the front wall platemember 114 is folded along the left side wall front end folding ruledline BL6 so that an angle therebetween becomes 90 degrees. Similarly,the front wall plate member 114 or the right side wall plate member 115is folded along the front wall right end folding ruled line BL7 so thatan angle therebetween becomes 90 degrees, and the right side wall platemember 115 or the right side rear margin 116 is folded along the rightside wall rear end folding ruled line BL5 so that an angle therebetweenbecomes 90 degrees.

Then, the right side rear margin 116 is glued to an inner face of aright end portion of the rear wall plate member 112 with a glue, forexample, to form side faces of the inverted quadrangular pyramid of thebox body 110. Also, the left side flap 130 is folded rightward, orinward, along the left side wall upper end folding ruled line BL3, andthe right side flap 140 is similarly folded leftward, or inward, alongthe right side wall upper end folding ruled line BL4. The openable lid111 is folded forward, or inward, along the openable base end foldingruled line BL1, and the insertion piece 120 is folded downward, orinward, along the openable front end edge folding ruled line BL2.

The packing box 100 has a slit lock engaging structure LK in which theopenable lid 111 is maintained in a closed state by engaging a part ofthe side flap into a slit created by partially cutting a connection baseend of the insertion piece 120 along the openable front end edge foldingruled line BL2. Specifically, a left L-shaped cut CT1 and a rightL-shaped cut CT2 exist in the vicinity of the openable front end edgefolding ruled line BL2 of the insertion piece 120. By folding theinsertion piece 120 along the openable front end edge folding ruled lineBL2 toward the openable lid 111, a left slit SL1 and a right slit SL2,which are gaps between the insertion piece 120 and the openable lid 111,are formed. In the present embodiment, due to a relatively largethickness of the material of the packing box 100, the slits (SL1 andSL2) are formed with the L-shaped cuts (CT1 and CT2). If the thicknessof the material of the packing box 100 is relatively small, however, theslits may be formed with simple straight cuts, or I-shaped cuts.

A left slit engaging piece 131 formed at a front end of the left sideflap 130 then enters into the left slit SL1, making the insertion piece120 being engaged by the left slit engaging piece 131 in the left slitSL1. Similarly, a right slit engaging piece 141 formed at a front end ofthe right side flap 140 enters into the right slit SL2, making theinsertion piece 120 being engaged by the right slit engaging piece 141in the right slit SL2.

In the present embodiment, a tear inducing line 111 d, which is aperforated line as one example, extends from a right flap opposing edge111 b, which is a flap opposing edge of the openable lid 111 opposingthe side flap, to a front end edge 111 c of the openable lid 111. A partof the openable lid 111 is torn along the tear inducing line 111 d andis raised up with respect to the openable lid 111 by a human hand toform a slit lock release gripping piece 111 e that can be used forreleasing the engagement by the slit lock engaging structure LK.

Behavior and function of the slit lock release gripping piece 111 e willnow be described. As illustrated in FIGS. 3A and 3B, when the openablelid 111 is opened from the state illustrated in FIG. 1, a part of theopenable lid 111 is torn from the right flap opposing edge 111 b of theopenable lid 111 along the tear inducing line 111 d due to a pullingforce in upward and forward directions created by a human hand and formsthe slit lock release gripping piece 111 e. At this moment, the slitlock release gripping piece 111 e takes a slightly raised position withrespect to the rest of the openable lid 111.

In the present embodiment, the tear inducing line 111 d is formed in anarc-like shape that is orthogonal to the right flap opposing edge 111 band the front end edge 111 c of the openable lid 111. Thus, when a partof the openable lid 111 is raised up from the right flap opposing edge111 b by a human hand, the direction of a stress acting on the tearinducing line 111 d gradually changes from the direction orthogonal tothe right flap opposing edge 111 b of the openable lid 111 to thedirection orthogonal to the front end edge 111 c of the openable lid111. Also, the point on which the stress acts does not stay on a singlelocation on the tear inducing line 111 d but moves gradually from theright flap opposing edge 111 b to the front end edge 111 c of theopenable lid 111 in an arc-like manner. That is, the tearing along thetear inducing line 111 d is executed smoothly.

Also, the arc-like shape of the tear inducing line 111 d is an arc of aprecise circle whose center is located at a cross-point CP of the frontend edge 111 c and the right flap opposing edge 111 b of the openablelid 111. Thus, when apart of the openable lid 111 is raised up from theright flap opposing edge 111 b of the openable lid 111 by a human hand,the amount of the stress acting along the tear inducing line 111 d issubstantially equalized in accordance with the radius of the precisecircle and a load acting from a human hand is also substantiallyhomogenized. That is, the tearing along the tear inducing line 111 d isexecuted more smoothly.

As illustrated in FIGS. 4A and 4B, the slit lock release gripping piece111 e is raised up from the state illustrated in FIGS. 3A and 3B due toa pulling force in upward and forward directions created by a humanhand. As illustrated in FIGS. 5A and 5B, the insertion piece 120 is alsopulled forward due to the pulling force created by a human hand from thestate illustrated in FIGS. 4A and 4B. Then, the right slit SL2, which isthe slit at a side of the insertion piece 120 in a lateral direction ofthe insertion piece 120 where the slit lock release gripping piece 111 eis formed, moves forward with respect to the right slit engaging piece141 of the right side flap 140, allowing the right slit engaging piece141 to be taken out of the right slit SL2.

That is, the engagement between the insertion piece 120 and the rightslit engaging piece 141 in the right slit SL2 is released. It is notedthat, because the packing box 100 has flexibility, the front wall platemember 114 deforms in a greater or lesser degree due to a forwardpulling force created by a human hand, allowing the right slit SL2 tomove forward.

As illustrated in FIGS. 6A and 6B, the slit lock release gripping piece111 e is pulled upward and forward from the state illustrated in FIGS.5A and 5B due to a pulling force in upward and forward directionscreated by a human hand. Then, the insertion piece 120 is also pulledupward and forward, causing the insertion piece 120 to move upward whilethe right slit engaging piece 141 is out of the right slit SL2.

As illustrated in FIGS. 7A and 7B, due to the pulling force in upwardand forward directions created by a human hand in the state illustratedin FIGS. 6A and 6B, the openable lid 111 starts to open while beingslightly twisted such that one side of the openable lid 111 in thelateral direction thereof where the slit lock release gripping piece 111e is formed precedes the other side of the openable lid 111 in thelateral direction thereof. At this point, the insertion piece 120 isinclined with respect to the lateral direction, and the engagementbetween the insertion piece 120 and the left slit engaging piece 131 ofthe left side flap 130 in the left slit SL1 at the other side of theopenable lid 111 in the lateral direction thereof is loosened.

The left slit SL1 then moves upward while being inclined with respect tothe left slit engaging piece 131 of the left side flap 130, causing theleft slit engaging piece 131 to be taken out of the left slit SL1. Thatis, the engagement between the insertion piece 120 and the left slitengaging piece 131 in the left slit SL1 is released.

Next, as illustrated in FIG. 8, due to an upward pulling force createdby a human hand in the state illustrated in FIGS. 7A and 7B, theinsertion piece 120 is taken out of the box body 110, and the openablelid 111 becomes an open state. As described above, because the pullingforce created by a human hand acts upward and forward and the directionof the pulling force does not need to be inverted, the slit lock can bereleased smoothly to open the openable lid 111. Also, a fancy box housedin the packing box 100 can be taken out of the packing box 100 withoutusing a tool such as a cutter.

Furthermore, as illustrated in FIGS. 9A to 9C, the right slit SL2 of theinvention is formed with the right L-shaped cut CT2 (see FIG. 2) and theinsertion piece 120 in a folded state with respect to the openable lid111. The right L-shaped cut CT2 is formed by cutting from a start pointon the openable front end edge folding ruled line BL2, which is a borderbetween the insertion piece 120 and the openable lid 111, toward a sideof the insertion piece 120 for a length that is at least equal to athickness dl of the right side flap 140 and then cutting toward a sideend of the insertion piece 120.

Also, a part of the openable lid 111 that projects forward from theopenable front end edge folding ruled line BL2, which is the borderbetween the insertion piece 120 and the openable lid 111, due to theright L-shaped cut CT2 when the insertion piece 120 is in the foldedstate with respect to the openable lid 111 forms an unlock projectionpiece 111 f, The unlock projection piece 111 f is configured so as toabut against the right slit engaging piece 141 in the right slit SL2when the slit lock release gripping piece 111 e is raised up to releasethe engagement created by the slit lock engaging structure LK.

Behavior and function of the unlock projection piece 111 f will now bedescribed. As illustrated in FIG. 9A, the right slit engaging piece 141enters into the right slit SL2 having a size that is at least equal tothe thickness dl of the right side flap 140 to engage the insertionpiece 120. Also, the unlock projection piece 111 f projects forward fromthe openable front end edge folding ruled line BL2.

As illustrated in FIG. 9B, the slit lock release gripping piece 111 e,which is a part of the openable lid 111, is torn along the tear inducingline 111 d from the state illustrated in FIG. 9A and gripped by a humanhand. Then, due to a pulling force acting in upward and forwarddirections created by a human hand, the slit lock release gripping piece111 e swings upward and forward around the openable front end edgefolding ruled line BL2. At this moment, the unlock projection piece 111f provided across the openable front end edge folding ruled line BL2from the slit lock release gripping piece 111 e swings downward andrearward so as to close the right slit SL2 and abuts against the rightslit engaging piece 141 in the right slit SL2.

The unlock projection piece 111 f then pushes the right slit engagingpiece 141 in the right slit SL2 rearward in a relative manner. At thismoment, due to a reaction force from the right slit engaging piece 141,the openable front end edge folding ruled line BL2 and the slit lockrelease gripping piece 111 e, the insertion piece 120 and the right slitSL2 in the vicinity of the openable front end edge folding ruled lineBL2 slightly moves forward and the front wall plate member 114 deflectsforward.

As illustrated in FIG. 9C, when the slit lock release gripping piece 111e further swings and is raised up by a human hand from the stateillustrated in FIG. 9B, the unlock projection piece 111 f closes theright slit SL2. Then, the unlock projection piece 111 f pushes a frontend of the right slit engaging piece 141, causing the openable front endedge folding ruled line BL2 and the slit lock release gripping piece 111e, the insertion piece 120, and the right slit SL2 in the vicinity ofthe openable front end edge folding ruled line BL2 to further moveforward and the front wall plate member 114 to further deflect forward.

Accordingly, the right slit engaging piece 141 in the right slit SL2 isrelatively pushed out of the right slit SL2, and the engagement betweenthe insertion piece 120 and the right slit engaging piece 141 in theright slit SL2 is released. In other words, because the unlockprojection piece 111 f is provided, the engagement between the insertionpiece 120 and the right slit engaging piece 141 in the right slit SL2 isreleased at a timing somewhere between FIGS. 4A and 5B, which makes iteasier to open the openable lid 111.

It is noted that the timing at which this engagement is completelyreleased depends on the relative positions of the insertion piece 120and the slit lock release gripping piece 111 e. That is, the engagementis completely released when the insertion piece 120 and the slit lockrelease gripping piece 111 e are approximately aligned on a straightline. Although in the present embodiment the slit lock release grippingpiece 111 e is provided only on the right side in the lateral direction,it may be provided on the left side as well, or even on both sides ofthe lateral direction. Also, although the openable lid 111 is providedupward for the purpose of description, it may be provided downward orsideways. Also, although in the present embodiment one face of thepolyhedron is adapted as the openable lid 111, multiple faces of thepolyhedron may be adapted as the openable lid 111, so that a pluralityof the openable lids 111 are provided.

Also, an open window may be formed on any one face of the polyhedron ofthe box body 110. This enables to see a product housed in the packingbox 100 from outside through the open window. Also, by housing a productso that a bar code of product information labeled on the product isaligned with the position of the open window, the bar code on theproduct housed in the packing box 100 can be seen from outside throughthe open window.

Furthermore, at least one of the slit lock release gripping piece 111 eand the right side flap 140, or the right side flap 140 in thisembodiment, has a temporary gluing portion 142 on a face thereofopposing the other of the slit lock release gripping piece 111 e and theright side flap 140, or the slit lock release gripping piece 111 e inthis embodiment. The temporary gluing portion 142 includes a glueapplied thereto for gluing to, removing from, and regluing to the other.This enables the slit lock release gripping piece 111 e to betemporarily glued so as to be in the same plane as the openable lid 111.

It is noted that, in the present embodiment, the insertion piece 120 isfolded for approximately 120 degrees so as to from an acute angle withrespect to the openable lid 111, and is inserted into the box body 110along an inner surface of the front wall plate member 114, which isarranged at an acute angle with respect to the openable lid 111. Whenthe angle between the openable lid 111 and the front wall plate member114 is an acute angle, a tip portion of the insertion piece 120 ispositioned closer to the base end of the openable lid 111 and the slitengaging piece of the side flap is inserted deeper into the slit incomparison with the case where the angle between the openable lid 111and the front wall plate member 114 is a right angle. Thus, it isdifficult to release the slit lock by inserting a human hand, or afingertip, between the insertion piece 120 and the front wall platemember 114. Therefore, when the angle between the openable lid 111 andthe front wall plate member 114 is an acute angle, the configurationincluding the slit lock release gripping piece 111 e is still effectiveeven if the interior of the box body 110 is not tightly filled.

Because the packing box 100 as the first embodiment of the inventionobtained as described above has a part of the openable lid 111 that canbe torn along the tear inducing line 113 d extending from the right flapopposing edge 111 b opposing the right side flap 140 to the front endedge 111 c of the openable lid 111 to form the slit lock releasegripping piece 111 e that can be used for releasing the engagement bythe slit lock engaging structure LK by being torn along the tearinducing line 111 d and raised up with respect to the openable lid 111by a human hand, the engagement by the slit lock engaging structure LK,which is the engagement between the insertion piece 120 and the rightside flap 140 in the right slit SL2 on the side in the lateral directionof the insertion piece 120 where the slit lock release gripping piece111 e is formed, can be easily released even if the interior of the boxbody 110 is tightly filled with a fancy box or the like.

Also, because the right slit SL2 is formed with the right L-shaped cutCT2 formed by cutting from a start point on the openable front end edgefolding ruled line BL2, which is a border between the insertion piece120 and the openable lid 111, toward a side of the insertion piece 120for a length that is at least equal to the thickness dl of the rightside flap 140 and then cutting toward a side end of the insertion piece120 and the insertion piece 120 folded with respect to the openable lid111, and a part of the openable lid 111 that projects forward from theopenable front end edge folding ruled line BL2, which is the borderbetween the insertion piece 120 and the openable lid 111, when theinsertion piece 120 is folded with respect to the openable lid 111 formsthe unlock projection piece 111 f that is able to abut against the rightslit engaging piece 141 in the right slit SL2 when the slit lock releasegripping piece 111 e is raised up to release the engagement created bythe slit lock engaging structure LK, the engagement by the slit lockengaging structure LK, which is the engagement between the insertionpiece 120 and the right side flap 140 in the right slit SL2 on the sidein the lateral direction of the insertion piece 120 where the slit lockrelease gripping piece 111 e is formed, can be reliably released.

Also, because the tear inducing line 111 d is formed in an arc-likeshape that is orthogonal to the right flap opposing edge 111 b and thefront end edge 111 c of the openable lid 111, the slit lock releasegripping piece 111 e can be formed by tearing along the tear inducingline 111 d smoothly.

Also, because the arc-like shape of the tear inducing line 111 d is anarc of a precise circle whose center is located at the cross-point CP ofthe front end edge 111 c and the right flap opposing edge 111 b of theopenable lid 111, the slit lock release gripping piece 111 e can beformed by tearing along the tear inducing line 111 d more smoothly.

Also, because an open window is formed on any one face of thepolyhedron, a user can check a product and a person in charge of productinspection, for example, can inspect a product.

Also, because at least one of the slit lock release gripping piece 111 eand the right side flap 140, or the right side flap 140 in thisembodiment, has a temporary gluing portion 142 on a face thereofopposing the other of the slit lock release gripping piece 111 e and theright side flap 140, or the slit lock release gripping piece 111 e inthis embodiment, and the temporary gluing portion 142 includes a glueapplied thereto for gluing to, removing from, and regluing to the other,the slit lock release gripping piece 111 e can be returned to theposition that is in the same plane as the openable lid 111, so that thepacking box 100 can be used continuously with the slit rock even afterthe packing box 100 is once open and the slit rock is re-released asneeded.

A packing box 200 of a second embodiment of the invention will now bedescribed with reference to FIGS. 10 and 11. FIG. 10 is a perspectiveview schematically illustrating the packing box 200 of the secondembodiment of the invention, and FIG. 11 is a development view of thepacking box 200 of the second embodiment of the invention.

The packing box 200 of the second embodiment is a modified version ofthe packing box 100 of the first embodiment where the number and shapeof the faces of the polyhedron are modified and has many elements thatare common with the packing box 100 of the first embodiment. Thus, thecommon elements will be identified with similar numbers in 200s and willnot be described in detail.

As illustrated in FIGS. 10 and 11, the packing box 200 as the secondembodiment of the invention is made of a thick coated cardboard, andincludes a box body 210 having a so-called semicyrindrical shape(octahedron) as one example of a polyhedron with two openable lid 211A,211B and being capable of housing a product (not shown), left side flaps230A, 230B and right side flaps 240A, 240B as side flaps, and insertionpieces 220A, 220B respectively holding the openable lids 211A, 211B.

In the description of the present embodiment, for the purpose ofillustration, the upside of the packing box 200 is where the openablelid 211A is located, the front side of the packing box 200 is where afront end edge 211Ac, which is a free end of the openable lid 211A, islocated, and the rear side of the packing box 200 is where a base end211Aa is located. The structure of a side of the openable lid 211B issimilar to the structure of a side of the openable lid 211A and thuswill not be described in detail.

The packing box 200 is constructed by folding inwardly along each offolding lines BL and grueling a margin 216 to an inner face of a rightside wall plate member 215 with a glue, for example, to form side facesof the semicylindrical shape (octahedron) of the box body 210. The restof the construction procedure is similar to that of the above-describedfirst embodiment and thus will not be described in detail.

Because the packing box 200 of the second embodiment of the inventionobtained as described above has a part of the openable lid 211A that canbe torn along a tear inducing line 211Ad extending from a right flapopposing edge 211Ab opposing the right side flap 240A to the front endedge 211Ac of the openable lid 211A to form a slit lock release grippingpiece 211Ae that can be used for releasing the engagement by the slitlock engaging structure LK by being torn along the tear inducing line211Ad and raised up with respect to the openable lid 211A by a humanhand, the engagement by the slit lock engaging structure LK, which isthe engagement between the insertion piece 220A and the right side flap240A in the right slit SL2 on the side in the lateral direction of theinsertion piece 220A where the slit lock release gripping piece 211Ae isformed, can be easily released even if the interior of the box body 210is tightly filled with a product.

A packing box 300 of a third embodiment of the invention will now bedescribed with reference to FIGS. 12 and 13. FIG. 12 is a perspectiveview schematically illustrating the packing box 300 of the thirdembodiment of the invention, and FIG. 13 is a development view of thepacking box 300 of the third embodiment of the invention.

The packing box 300 of the third embodiment is a modified version of thepacking box 200 of the second embodiment where some faces of thepolyhedron are modified as curved faces and has many elements that arecommon with the packing box 200 of the second embodiment. Thus, thecommon elements will be identified with similar numbers in 300s and willnot be described in detail.

As illustrated in FIGS. 12 and 13, the packing box 300 of the thirdembodiment of the invention is made of a thick coated cardboard, andincludes a box body 310 having a so-called semicyrindrical shape(including two curved faces plus six flat faces) as one example of apolyhedron with two openable lid 311A, 311B and two curved faces andbeing capable of housing a product (not shown), left side flaps 330A,330B and right side flaps 340A, 340B as side flaps, and insertion pieces320A, 320B respectively holding the openable lids 311A, 311B. In thedescription of the present embodiment, for the purpose of illustration,the upside of the packing box 300 is where the openable lid 311A islocated, the front side of the packing box 300 is where a front end edge311Ac, which is a free end of the openable lid 311A, is located, and therear side of the packing box 300 is where a base end 311Aa is located.The structure of a side of the openable lid 311B is similar to thestructure of a side of the openable lid 311A and thus will not bedescribed in detail.

The packing box 300 is constructed by folding a rear left curved surface317 and a rear right curved surface 318 in an arc-like shape, foldingother parts of the packing box 300 inwardly along each of folding linesBL, and grueling a margin 316 to an inner face of a right side wallplate member 315 with a glue, for example, to form side faces of thesemicylindrical shape (having two curved faces plus six flat faces) ofthe box body 310. The rest of the construction procedure is similar tothat of the above-described second embodiment and thus will not bedescribed in detail.

Because the packing box 300 of the third embodiment of the inventionobtained as described above has a part of the openable lid 311A that canbe torn along a tear inducing line 311Ad extending from a right flapopposing edge 311Ab opposing the right side flap 340A to the front endedge 311Ac of the openable lid 311 to form a slit lock release grippingpiece 311Ae that can be used for releasing the engagement by the slitlock engaging structure LK by being torn along the tear inducing line311Ad and raised up with respect to the openable lid 311A by a humanhand, the engagement by the slit lock engaging structure LK, which isthe engagement between the insertion piece 320A and the right side flap340A in the right slit SL2 on the side in the lateral direction of theinsertion piece 320A where the slit lock release gripping piece 311Ae isformed, can be easily released even if the interior of the box body 310is tightly filled with a product. That is, even though the box body 310of the packing box 300 is a polyhedron having curved faces such as therear left curved surface 317 and the rear right curved surface 318, thesame effects as the above-described second embodiment can be obtained.

A packing box 400 of a fourth embodiment of the invention will now bedescribed with reference to FIGS. 14 and 15. FIG. 14 is a perspectiveview schematically illustrating the packing box 400 of the fourthembodiment of the invention, and FIG. 15 is a development view of thepacking box 400 of the fourth embodiment of the invention.

The packing box 400 of the fourth embodiment is a modified version ofthe packing box 100 of the first embodiment where the number and shapeof faces of the polyhedron as well as the number of the openable lids111 are modified and has many elements that are common with the packingbox 100 of the first embodiment. Thus, the common elements will beidentified with similar numbers in 400s and will not be described indetail.

As illustrated in FIGS. 14 and 15, the packing box 400 of the fourthembodiment of the invention is made of a thick coated cardboard, andincludes a box body 410 that is a so-called rhombicuboctahedron(icosihexahedron) as one example of a polyhedron having two openable lid411A, 411B and being capable of housing a product (not shown), left sideflaps 430A, 430B and right side flaps 440A, 440B as side flaps, andinsertion pieces 420A, 420B respectively holding the openable lids 411A,411B. In the description of the present embodiment, for the purpose ofillustration, the upside of the packing box 400 is where the openablelid 411A is located, the front side of the packing box 400 is where afront end edge 411Ac, which is a free end of the openable lid 411A, islocated, and the rear side of the packing box 200 is where a base end411Aa is located. The structure of a side of the openable lid 411B issimilar to the structure of a side of the openable lid 411A and thuswill not be described in detail.

The packing box 400 is constructed by folding inward along each offolding lines BL, grueling each triangular margin 416A adjacent to atriangular face to an inner face of a rectangular plate members 412adjacent to the triangular margins 416A with a glue, for example, andgrueling a rectangular margin 416B to an inner face of a rear right sideplate member 419 with a glue, for example. The left side flap 430A andthe right side flap 440A are then folded inward, and an insertion piece420A of the openable lid 411A is inserted into the box body 410 to formthe rhombicuboctahedron (icosihexahedron) of the box body 410.

It is noted that, in the present embodiment, the insertion piece 420A isfolded at approximately 45 degrees so as to form an obtuse angle withrespect to the openable lid 411A, and is inserted into the box body 410along an inner surface of the front wall plate member 414, which isarranged at an obtuse angle with respect to the openable lid 411A. Whenthe angle between the openable lid 411A and the front wall plate member414 is an obtuse angle, it is difficult to insert a human hand, orparticularly a fingertip, between the insertion piece 420 and the frontwall plate member 414, because a force does not act on the front wallplate member 414 in a direction to widen a space between the insertionpiece 420 and the front wall plate member 414. Therefore, when the anglebetween the openable lid 411A and the front wall plate member 414 is anobtuse angle, the configuration including a slit lock release grippingpiece 411Ae is still effective even if the interior of the box body 140is not tightly filled.

Because the packing box 400 of the fourth embodiment of the inventionobtained as described above has apart of the openable lid 411A that canbe torn along a tear inducing line 411Ad extending from a left flapopposing edge 411Ab opposing a left side flap 430A to a front end edge411Ac of the openable lid 411A to form the slit lock release grippingpiece 411Ae that can be used for releasing the engagement by the slitlock engaging structure LK by being torn along the tear inducing line411Ad and raised up with respect to the openable lid 411A by a humanhand, the engagement by the slit lock engaging structure LK, which isthe engagement between the insertion piece 420A and the left side flap430A in the left slit SL1 on the side in the lateral direction of theinsertion piece 420A where the slit lock release gripping piece 411Ae isformed, can be easily released even if the interior of the box body 410is tightly filled with a product.

A packing box 500 of a fifth embodiment of the invention will now bedescribed with reference to FIGS. 16 to 24. FIG. 16 is a frontperspective view schematically illustrating the packing box 500 of thefifth embodiment of the invention. FIG. 17 is a development view of thepacking box 500 of the fifth embodiment of the invention. FIGS. 18A,19A, 20A, 21A, and 22A are front perspective views illustrating thebehavior of a slit lock release gripping invention. FIGS. 18B, 19B, 20B,21B, and 22B are rear perspective views respectively corresponding toFIGS. 18A, 19A, 20A, 21A, and 22A. FIG. 23 is a front perspective viewillustrating the state in which a top face lid 540, which is an openablelid of the packing box 500 of the invention, is open. FIG. 24A is asectional side view as seen in the direction represented with referencenumerals 24B-24B in FIG. 18A. FIG. 24B is a sectional side view as seenin the direction represented with reference numerals 24B-24B in FIG.18A. FIG. 24C is a sectional side view as seen in the directionrepresented with reference numerals 24C-24C in FIG. 19A.

As illustrated in FIGS. 16 and 17, the packing box 500 of the fifthembodiment of the invention is made of a thick coated cardboard, andincludes an openable lid 540 that constitutes at least one face of a boxbody 510 for housing a product and that is freely swung around a baseend to seal a product taking-in/out opening formed at a position of theone face, side flaps 520, 530 that are laterally positioned with respectto the openable lid 540 and are respectively connected to openable lidside edge portions of lid side members constituting parts of apolyhedron via a folding line to prevent protrusion of the product, andan insertion piece that is connected to a front end edge of the openablelid 540 via a folding line and that is inserted into the box body 510 tohold the openable lid 540. In other words, the packing box 500 includesthe box body 510 to house a fancy box (not shown) as one example of theproduct, the right flap 520 and the left flap 530 as side flaps forpreventing protrusion of the fancy box, the openable lid 540 consistingof the top face lid to openably seal an upper end portion of the boxbody 510, and an insertion piece 550 that is inserted into the box body510 to hold the top face lid 540. In the description of the presentembodiment, “left” and “right” are left and right with respect to thepacking box 500 that has been constructed. In other words, “left” and“right” are left and right of the packing box 500 as seen from a rearwall plate member 512 toward a front wall plate member 511 of thepacking box 500.

As illustrated in FIG. 17, the box body 510 includes the front wallplate member 511, the rear wall plate member 512, a plurality of sidewall plate members including a right side wall plate member 513 and aleft side wall plate member 514, a rear wall margin 515, and bottomplate members including a front side bottom plate member 516, a rearside bottom plate member 517, a right bottom plate member 518 and a leftbottom plate member 519. The right side wall plate member 513 isconnected to a right end portion of the front wall plate member 511 viaa wall right end folding ruled line BL11, which is a folding line. Therear wall plate member 512 is connected to a rear end portion of theright side wall plate member 513 via a rear wall right end folding ruledline BL12, which is a folding line.

The left side wall plate member 514 is connected to a left end portionof the front wall plate member 511 via a front wall left end foldingruled line BL13, which is a folding line. The rear wall margin 515 isconnected to a left end portion of the rear wall plate member 512 via arear wall left end folding ruled line BL14, which is a folding line. Thefront side bottom plate member 516 is connected to a lower end portionof the front wall plate member 511 via a front wall lower end foldingruled line BL15, which is a folding line. Also, the front side bottomplate member 516 includes a front side bottom base 516 a, a front sidebottom margin 516 b, and a front side bottom tongue piece 516 c, and thefront side bottom margin 516 b is connected to the front side bottombase 516 a via a front side bottom folding ruled line BL16, which is afolding line.

Similar to the front side bottom plate member 516, the rear side bottomplate member 517 is connected to a lower end of the rear wall platemember 512 via a rear wall lower end folding ruled line BL17, which is afolding line. Also, the rear side bottom plate member 517 includes arear side bottom base 517 a, a rear side bottom margin 517 b, and a rearside bottom tongue piece 517 c, and the rear side bottom margin 517 b isconnected to the rear side bottom base 517 a via a rear side bottomfolding ruled line BL18, which is a folding line. The right bottom platemember 518 is connected to a lower end of the right side wall platemember 513 via a right side wall lower end folding ruled line BL19,which is a folding line. Similar to right bottom plate member 518, theleft bottom plate member 519 is connected to a lower end of the leftside wall plate member 514 via a left side wall lower end folding ruledline BL20, which is a folding line.

When the packing box 500 is constructed, the front wall plate member 511and the right side wall plate member 513 are folded with respect to eachother along the front wall right end folding ruled line BL11 so that anangle therebetween becomes 90 degrees, and the right side wall platemember 513 and the rear wall plate member 512 are folded with respect toeach other along the rear wall right end folding ruled line BL12 so thatan angle therebetween becomes 90 degrees, for example. Similarly, thefront wall plate member 511 and the left side wall plate member 514 arefolded with respect to each other along the front wall left end foldingruled line BL13 so that an angle therebetween becomes 90 degrees, andthe rear wall plate member 512 and the rear wall margin 515 are foldedwith respect to each other along the rear wall left end folding ruledline BL14 so that an angle therebetween becomes 90 degrees.

Then, the rear wall margin 515 is glued to a rear end portion of aninner face of the left side wall plate member 514 with a glue, forexample, making the outer circumference of the box body 510 rectangularin a planar view. Next, the box body 510 is temporarily deformed so thatthe cross section of the box body 510 in a planar view becomes aparallelogram, and the front side bottom margin 516 b is glued to anouter face of the left bottom plate member 519 with a glue, for example.Similarly, the rear side bottom margin 517 b is glued to an outer faceof the right bottom plate member 518 with a glue, for example.

Then, the deformed the box body 510 is returned to the original state sothat the shape of the cross section of the box body 510 in a planar viewchanges from the parallelogram to a rectangle having right angles.Accordingly, the front side bottom plate member 516, which is foldedalong the front side bottom folding ruled line BL16, becomes unfoldedand the rear side bottom plate member 517, which is folded along therear side bottom folding ruled line BL18, also becomes unfolded. Also,the front side bottom tongue piece 516 c is inserted into an inner faceside of the rear side bottom base 517 a and the rear side bottom tonguepiece 517 c is also inserted into an inner face side of the front sidebottom base 516 a. Then, the front side bottom tongue piece 516 c andthe rear side bottom tongue piece 517 c engage with each other, and anedge portion of the front side bottom base 516 a and an edge portion ofthe rear side bottom base 517 a engage with each other, making the boxbody 510 stable in a state where the cross section of the box body 510in a planar view is rectangular, or where the box body 510 is able tohouse a fancy box.

Also, the right side flap 520 is connected to the openable lid side edgeportion of the lid side member, that is, an upper end portion of theright side wall plate member 513, via a right side wall upper endfolding ruled line BL21, which is a folding line. Similarly, the leftside flap 530 is connected to the openable lid side edge portion of thelid side member, that is, an upper end portion of the left side wallplate member 514, via a left side wall upper end folding ruled lineBL22, which is a folding line. A base end of the top face lid 540, whichis an openable lid, is connected to an upper end portion of the rearwall plate member 512 via a rear wall upper end folding ruled line BL23,which is a folding line. The insertion piece 550 is connected to a frontend edge 542 of the top face lid 540 via a top face front end edgefolding ruled line BL24, which is a folding line.

The packing box 500 has a slit lock engaging structure LK in which theopenable lid 540, or the top face lid, is maintained in a closed stateby engaging a part of the side flap into a slit created by partiallycutting a connection base end of the insertion piece 550 along the topface front end edge folding ruled line BL24. Specifically, a rightL-shaped cut CT11 and a left L-shaped cut CT22 exist in the vicinity ofthe top face front end edge folding ruled line BL24 of the insertionpiece 550. By folding the insertion piece 550 along the top face frontend edge folding ruled line BL24 toward the top face lid 540, a rightslit SL11 and a left slit SL22, which are gaps between the insertionpiece 550 and the top face lid 540, are formed. In the presentembodiment, due to a relatively large thickness of the material of thepacking box 500, the slits (SL11 and SL22) are formed with the L-shapedcuts (CT11 and CT22). If the thickness of the material of the packingbox 500 is relatively small, however, the slits may be formed withsimple straight cuts, or I-shaped cuts.

A right slit engaging piece 521 formed at a front end of the right sideflap 520 then enters into the right slit SL11, making the insertionpiece 550 being engaged by the right slit engaging piece 521 in theright slit SL11. Similarly, a left slit engaging piece 531 formed at afront end of the left side flap 530 enters into the left slit SL22,making the insertion piece 550 being engaged by the left slit engagingpiece 531 in the left slit SL22.

In the present embodiment, a tear inducing line 543, which is aperforated line, for example, extends from a left flap opposing edge541, which is a flap opposing edge of the top face lid 540 as anopenable lid, to a front end edge 542 of the top face lid 540. A part ofthe top face lid 540 can be torn along the tear inducing line 543 and beraised up with respect to top face lid 540 by a human hand to form aslit lock release gripping piece 544 that can be used for releasing theengagement by the slit lock engaging structure LK.

Behavior and function of the slit lock release gripping piece 544 willnow be described. As illustrated in FIGS. 18A and 18B, when the top facelid 540 is opened from the state illustrated in FIG. 16, a part of thetop face lid 540 is torn from the left flap opposing edge 541 of topface lid 540 due to a pulling force in upward and forward directionscreated by a human hand and forms the slit lock release gripping piece544. At this moment, the slit lock release gripping piece 544 takes aslightly raised position with respect to the rest of the top face lid540.

In the present embodiment, the tear inducing line 543 is formed in anarc-like shape that is orthogonal to the left flap opposing edge 541 andthe front end edge 542 of the top face lid 540 as an openable lid. Thus,when a part of the top face lid 540 is raised up from the left flapopposing edge 541 of the top face lid 540 by a human hand, the directionof a stress acting on the tear inducing line 543 gradually changes fromthe direction orthogonal to the left flap opposing edge 541 to thedirection orthogonal to the front end edge 542 of the top face lid 540.Also, the point on which the stress acts does not stay on a singlelocation on the tear inducing line 543 but moves gradually from the leftflap opposing edge 541 to the front end edge 542 of top face lid 540 inan arc-like manner. That is, the tearing along the tear inducing line543 is executed smoothly.

Also, the arc-like shape of the tear inducing line 543 is an arc of aprecise circle whose center is located at a cross-point CP of the frontend edge 542 and the left flap opposing edge 541 of the top face lid540. Thus, when a part of the top face lid 540 is raised up from theleft flap opposing edge 541 of the top face lid 540 by a human hand, theamount of the stress acting along the tear inducing line 543 issubstantially equalized in accordance with the radius of the precisecircle and a load acting from a human hand is also substantiallyhomogenized. That is, the tearing along the tear inducing line 543 isexecuted more smoothly.

As illustrated in FIGS. 19A and 19B, the slit lock release grippingpiece 544 is raised up from the state illustrated in FIGS. 18A and 18Bdue to a pulling force in upward and forward directions created by ahuman hand. As illustrated in FIGS. 20A and 20B, the insertion piece 550is also pulled forward due to the pulling force created by a human handfrom the state illustrated in FIGS. 19A and 19B. Then, the left slitSL22, which is the slit at a side of insertion piece 550 in a lateraldirection of the insertion piece 550 where slit lock release grippingpiece 544 is formed, moves forward with respect to the left slitengaging piece 531 of the left side flap 530, allowing the left slitengaging piece 531 to be taken out of the left slit SL22.

That is, the engagement between the insertion piece 550 and the leftslit engaging piece 531 in the left slit SL22 is released. It is notedthat, because the packing box 500 has flexibility, the front wall platemember 511 deforms in a greater or lesser degree due to a forwardpulling force created by a human hand, allowing the left slit SL22 tomove forward.

As illustrated in FIGS. 21A and 21B, the slit lock release grippingpiece 544 is pulled upward and forward from the state illustrated inFIGS. 20A and 20B due to the pulling force in upward and forwarddirections created by a human hand. Then, the insertion piece 550 isalso pulled upward and forward, causing the insertion piece 550 to moveupward while the left slit engaging piece 531 is out of the left slitSL22.

As illustrated in FIGS. 22A and 22B, due to the pulling force in upwardand forward directions created by a human hand in the state illustratedin FIGS. 21A and 21B, the top face lid 540 starts to open while beingslightly twisted such that one side of the top face lid 540 in thelateral direction thereof where the slit lock release gripping piece 544is formed precedes the other side of the top face lid 540 in the lateraldirection thereof. At this point, the insertion piece 550 is inclinedwith respect to the lateral direction, and the engagement between theinsertion piece 550 and the right slit engaging piece 521 of the rightside flap 520 in the right slit SL11 at the other side of the top facelid 540 in the lateral direction thereof is loosened.

The right slit SL11 then moves upward while being inclined with respectto the right slit engaging piece 521 of the right side flap 520, causingright slit engaging piece 521 to be taken out of the right slit SL11.That is, the engagement between the insertion piece 550 and the rightslit engaging piece 521 in the right slit SL11 is released.

Next, as illustrated in FIG. 23, due to an upward pulling force createdby a human hand in the state illustrated in FIGS. 22A and 22B, theinsertion piece 550 is taken out of the box body 510, and the top facelid 540 becomes an open state. As described above, because the pullingforce created by a human hand acts upward and forward and the directionof the pulling force does not need to be inverted, the slit lock can bereleased smoothly to open the top face lid 540. Also, a fancy box housedin the packing box 500 can be taken out of the packing box 500 withoutusing a tool such as a cutter.

Furthermore, as illustrated in FIGS. 24A to 24C, the left slit SL22 ofthe invention is formed with the left L-shaped cut CT22 (see FIG. 17)and the insertion piece 550 in a folded state with respect to the topface lid 540. The left L-shaped cut CT22 is formed by cutting from astart point on the top face front end edge folding ruled line BL24,which is a border between the insertion piece 550 and the top face lid540, toward a side of the insertion piece 550 for a length that is atleast equal to a thickness dl of the left side flap 530 and then cuttingtoward a side end of the insertion piece 550.

Also, a part of the top face lid 540 that projects forward from the topface front end edge folding ruled line BL24, which is the border betweenthe insertion piece 550 and the top face lid 540, due to the leftL-shaped cut CT22 while the insertion piece 550 is in the folded statewith respect to the top face lid 540 forms an unlock projection piece545. The unlock projection piece 545 is configured so as to abut againstthe left slit engaging piece 531 in the left slit SL22 when the slitlock release gripping piece 544 is raised up to release the engagementcreated by the slit lock engaging structure LK.

Behavior and function of the unlock projection piece 545 will now bedescribed. As illustrated in FIG. 24A, the left slit engaging piece 531enters into the left slit SL22 having a size that is at least equal tothe thickness dl of the left side flap 530 to engage the insertion piece550. Also, the unlock projection piece 545 projects forward from the topface front end edge folding ruled line BL24.

As illustrated in FIG. 24B, the slit lock release gripping piece 544,which is a part of the top face lid 540, is torn along the tear inducingline 543 from the state illustrated in FIG. 24A and gripped by a humanhand. Then, due to a pulling force acting in upward and forwarddirections created by a human hand, the slit lock release gripping piece544 swings upward and forward around the top face front end edge foldingruled line BL24. At this moment, the unlock projection piece 545provided across the top face front end edge folding ruled line BL24 fromthe slit lock release gripping piece 544 swings downward and rearward soas to close the left slit SL22 and abuts against left slit engagingpiece 531 in the left slit SL22.

The unlock projection piece 545 then pushes the left slit engaging piece531 in the left slit SL22 rearward in a relative manner. At this moment,due to a reaction force from the left slit engaging piece 531, the topface front end edge folding ruled line BL24 and the slit lock releasegripping piece 544, the insertion piece 550 and the left slit SL22 inthe vicinity of the top face front end edge folding ruled line BL24slightly moves forward and the front wall plate member 511 deflectsforward.

As illustrated in FIG. 24C, when the slit lock release gripping piece544 further swings and is raised up by a human hand from the stateillustrated in FIG. 24B, the unlock projection piece 545 closes the leftslit SL22. Then, the unlock projection piece 545 pushes a front end ofthe left slit engaging piece 531, causing the top face front end edgefolding ruled line BL24 and the slit lock release gripping piece 544,the insertion piece 550, and the left slit SL22 in the vicinity of thetop face front end edge folding ruled line BL24 to further move forwardand the front wall plate member 511 to further deflect forward.

Accordingly, the left slit engaging piece 531 in the left slit SL22 isrelatively pushed out of the left slit SL22, and the engagement betweenthe insertion piece 550 and the left slit engaging piece 531 in the leftslit SL22 is released. In other words, because the unlock projectionpiece 545 is provided, the engagement between the insertion piece 550and the left slit engaging piece 531 in the left slit SL22 is releasedat a timing illustrated in the above-described FIGS. 19A and 19B, makingit easier to open the top face lid 540.

Also, as illustrated in FIGS. 18A, 19A, 20A, and 21A, in the presentembodiment a cutout portion 511 a having an arc-like shape as oneexample is provided in an upper end portion of the front wall platemember 511 so as to oppose the tear inducing line 543 at the front endedge 542 of the top face lid 540. Thus, when the slit lock releasegripping piece 544 is pulled upward and forward by a pulling force, aportion of the front wall plate member 511 near the slit lock releasegripping piece 544 can easily deflect forward and the insertion piece550 can be easily displaced forward. Also, when the slit lock releasegripping piece 544 is pulled upward and forward by a pulling force,stress acting on an end point of the tear inducing line 543, which is ajoint portion between the slit lock release gripping piece 544 and theinsertion piece 550, is dispersed. That is, a break that tends to occurat this point is suppressed. The shape of the cutout portion 511 a isnot restricted to the arc-like shape: it may be a V-shape or a U-shape,for example.

Although in the present embodiment slit lock release gripping piece 544is provided only on the left side in the lateral direction, it may beprovided on the right side or even on both sides of the lateraldirection.

Because the packing box 500 of the fifth embodiment of the inventionobtained as described above has a part of the top face lid 540 that canbe torn along the tear inducing line 543 extending from the left flapopposing edge 541, which is a flap opposing edge of the top face lid540, to the front end edge 542 of the top face lid 540 to form the slitlock release gripping piece 544 that can be used for releasing theengagement by the slit lock engaging structure LK by being torn alongthe tear inducing line 543 and raised up with respect to the top facelid 540 by a human hand, the engagement by the slit lock engagingstructure LK, which is the engagement between the insertion piece 550and the left side flap 530 in the left slit SL22 on the side in thelateral direction of the insertion piece 550 where the slit lock releasegripping piece 544 is formed, can be easily released even if theinterior of the box body 510 is tightly filled with a fancy box or thelike.

Also, because the left slit SL22 is formed with the left L-shaped cutCT22 formed by cutting from a start point on the top face front end edgefolding ruled line BL24, which is a border between the insertion piece550 and the top face lid 540, toward a side of the insertion piece 550for a length that is at least equal to the thickness dl of the side flapand then cutting toward a side end of the insertion piece 550 and theinsertion piece 520 folded with respect to the top face lid 540, and apart of the top face lid 540 that projects forward from the openablefront top face front end edge folding ruled line BL24, which is theborder between the insertion piece 550 and the top face lid 540, whenthe insertion piece 520 is folded with respect to the top face lid 540forms the unlock projection piece 545 that is able to abut against theleft side flap 530 in the slit when the slit lock release gripping piece544 is raised up to release the engagement created by the slit lockengaging structure LK, the engagement by the slit lock engagingstructure LK, which is the engagement between the insertion piece 550and the left side flap 530 in the left slit SL22 on the side in thelateral direction of the insertion piece 550 where the slit lock releasegripping piece 544 is formed, can be reliably released.

Also, because the tear inducing line 543 is formed in an arc-like shapethat is orthogonal to the left flap opposing edge 541 and front end edge542 of the top face lid 540, the slit lock release gripping piece 544can be formed by tearing along the tear inducing line 543 smoothly.

Also, because the arc-like shape of the tear inducing line 543 is an arcof a precise circle whose center is located at the cross-point CP of thefront end edge 542 and the left flap opposing edge 541 of the top facelid 540, the slit lock release gripping piece 544 can be formed bytearing along the tear inducing line 543 more smoothly.

Also, because the cutout portion 511 a is provided in the upper endportion of the front wall plate member 511 so as to oppose the tearinducing line 543 at the front end edge 542 of the top face lid 540, theengagement by the slit lock engaging structure LK on the side in thelateral direction of the insertion piece 550 where the slit lock releasegripping piece 544 is formed can be released more easily, and a breakthat tends to occur at this point can be suppressed so that theengagement between the insertion piece 550 and the left side flap 530 inthe left slit SL22 created by the slit lock engaging structure LK can bemore reliably released.

A packing box 600 of a sixth embodiment of the invention will now bedescribed with reference to FIG. 25A. FIG. 25A is a front perspectiveview illustrating the packing box 600 of the sixth embodiment of theinvention. The packing box 600 of the sixth embodiment is a modifiedversion of the packing box 500 of the fifth embodiment in which a flapopposing edge cutout 646 is formed at a position where the tear inducingline 543 reaches the left flap opposing edge 541 of the top face lid540, and has many elements that are common with the packing box 500 ofthe fifth embodiment. Thus, the common elements will be identified withsimilar numbers in 600s and will not be described in detail.

As illustrated in FIG. 25A, the packing box 600 of the sixth embodimentof the invention has the flap opposing edge cutout 646 that is formed ata position where a tear inducing line 643 reaches a left flap opposingedge 641 of a top face lid 640. This enables the flap opposing edgecutout 646 to function as a mark. As a result, a start position fortearing along the tear inducing line 643 becomes easily visible.

Also, a fingertip of a human hand can easily catch on the flap opposingedge cutout 646, making it easier to insert the fingertip between a slitlock release gripping piece 644, which is a part of the top face lid640, and a left side flap 630. As a result, the slit lock releasegripping piece 644 can be easily torn along tear inducing line 643 andraised up.

A packing box 700 of a seventh embodiment of the invention will now bedescribed with reference to FIG. 25B. FIG. 25B is a front perspectiveview illustrating the packing box 700 of the seventh embodiment of theinvention. The packing box 700 of the seventh embodiment is a modifiedversion of the packing box 500 of the fifth embodiment where a flapopposing edge projecting piece 747 is formed on the left flap opposingedge 541 in a portion anterior to the tear inducing line 543 on the topface lid 540, and has many elements that are common with the packing box500 of the fifth embodiment. Thus, the common elements will beidentified with similar numbers in 700s and will not be described indetail.

As illustrated in FIG. 25B, the packing box 700 of the sixth embodimentof the invention has the flap opposing edge projecting piece 747 that isformed on a left flap opposing edge 741 in a portion anterior to a tearinducing line 743 on a top face lid 740. The flap opposing edgeprojecting piece 747 projects in a left side of the lateral direction.This enables the flap opposing edge projecting piece 747 to function asa mark. As a result, a start position for tearing along the tearinducing line 743 becomes easily visible.

Also, a fingertip of a human hand can easily catch on the flap opposingedge projecting piece 747, making it easier to insert the fingertipbetween a flap opposing edge projecting piece 747, which is a part ofthe top face lid 740, and a left side flap 730. As a result, the slitlock release gripping piece 744 can be easily torn along tear inducingline 743 and raised up. It will be more effective if the flap opposingedge projecting piece 747 slightly projects from a face of the left sidewall plate member 714.

A packing box 800 of an eighth embodiment of the invention will now bedescribed with reference to FIG. 26. FIG. 26 is a development view of anupper part of the packing box of the eighth embodiment of the invention.The packing box 800 of the eighth embodiment is a modified version ofthe packing box 500 of the fifth embodiment having a hexagonal-columnshape, and has many elements that are common with the packing box 500 ofthe fifth embodiment. Thus, the common elements will be identified withsimilar numbers in 800s and will not be described in detail.

As illustrated in FIG. 26, the packing box 800 having a hexagonal-columnshape of the eighth embodiment of the invention includes a front wallplate member 811, a rear wall plate member 812, a right side wall platemember 813 a, a right side wall plate member 813 b, a left side wallplate member 814 a, a left side wall plate member 814 b, and a side wallmargin 815. It is noted that the packing box 800 having ahexagonal-column shape can tightly house fancy boxes having atriangular-column shape or fancy boxes having a quadrangular-columnshape whose cross-section as seen in a plan view is a rhombus.

The side wall margin 815 is glued to an inner face of the front wallplate member 811 with a glue, for example. The top face lid 840 has twoinsertion pieces 850 a, 850 b connected thereto. The insertion piece 850b is slit-locked by a right slit engaging piece 821 of a right side flap820 connected to an upper end portion of the right side wall platemember 813 a. Similarly, the insertion piece 850 a is slit-locked by aleft slit engaging piece 831 of a left side flap 830 connected to anupper end portion of the left side wall plate member 814 a.

Also, each of the insertion pieces 850 a, 850 b is slit-locked by a partof a front flap 860 connected to an upper end portion of the front wallplate member 811. Two tear inducing lines 843 a, 843 b are provided. Thetear inducing line 843 a extends from a left flap opposing edge 841 a toa left insertion piece side edge portion 842 a, and the tear inducingline 843 b extends from a right flap opposing edge 841 b to a rightinsertion piece side edge portion 842 b.

As with the above-described embodiments, parts of the top face lid 840as openable lids are torn along the tear inducing lines 843 a, 843 bwith a pulling force created by a human hand to form slit lock releasegripping pieces 844 a, 844 b. Accordingly, the engagement by the slitlock engaging structure LK, which is the engagement between theinsertion piece 850 a and the left side flap 830 in a slit or theengagement between the insertion piece 850 b and the right side flap 820in a slit, can be released. The mechanism of releasing the slit lock issimilar to those of the above-described embodiments and is thus notdescribed in detail.

INDUSTRIAL APPLICABILITY

The invention particularly relates to a packing box that packs a productitself, such as a cosmetic, drug, food, or toy, or a fancy box thathouses the product and is displayed on a sales floor, such as a storefront, for protecting the product or the fancy box from being damaged orimpacted during delivery of the product or the fancy box to the salesfloor.

What is claimed is:
 1. A method for opening a packing box, wherein thepacking box comprises: a box body for housing a product, the box bodyhaving a front wall plate member, a rear wall plate member, and aplurality of side wall plate members; a side flap that is connected viaa first folding line to an upper end portion of the side wall platemembers for preventing protrusion of the product; a top face lid that isconnected via a folding line to an upper end portion of the rear wallplate member for openably sealing an upper end portion of the box body;and an insertion piece that is connected to a front end edge of the topface lid via a third folding line and is inserted into the box body forholding the top face lid, the packing box having a slit lock engagingstructure that maintains a state in which the top face lid is closed byengaging a part of the side flap into a slit created by cutting a partof a connection base end of the insertion piece along the direction ofsaid third folding line; and wherein the slit is formed by an L-shapedcut having a first leg extending perpendicularly from said folding line,the length of said first leg being at least as great as the thickness ofthe side flap, and a second leg extending in the direction of said thirdfolding line to a side end of the insertion piece, the insertion piecebeing folded along said third folding line with respect to the top facelid for forming the slit; and wherein the packing box is opened by:manually gripping a part of the top face lid and tearing said part ofthe top face lid along a tear inducing line extending from a side flapopposing edge of the top face lid to a front end edge of the top facelid; manually raising said part of the top face lid up with respect tothe top face lid, thereby forming a slit lock release gripping piece;and manually pulling forward and upward on said slit lock releasegripping piece to release engagement created by the slit lock engagingstructure.
 2. The method according to claim 1, wherein said first leg ofthe L-shaped slit extends rearward from said second leg toward said rearwall plate member, and wherein a part of the top face lid projectingforward from the folding line when the insertion piece is folded withrespect to the top face lid forms an unlock projection piece, andwherein, when said slit lock release gripping piece is pulled forwardand upward, said unlock projection piece abuts a said part of the sideflap, and thereby releases the engagement created by the slit lockengaging structure.